Why can’t he see that no-one fancies him because he’s awkward and stiff and cringy and entitled and arrogant and condescending
Well to be fair to him, I don't think anyone should hate themselves that much. 
Don't get me wrong, he probably is all those things to a certain degree, but he probably also has some very good qualities, kindness, Intelligence, loyalty, sense of humour etc.
I don't think Ellie has treated him fairly to be honest, I just don't understand why. I'd get it if it changed over a few days, but it literally changed as soon as she recoupled, she made it clear she wanted nothing to do with him immediately after,
It looks very much like she knew he was guaranteed to pick her, so used him to stay in.